This invention relates to a sonic or sine generator drilling head for use on a drill rig.
Soil samples may be taken by at least two methods: drilling and by directly driving samplers into the earth. Sonic drilling is a method of driving a sampler in which vibratory energy is applied to the drill rod. This technique is particularly effective when the vibrations coincide with the natural resonant frequency of the drill rod or casing, because the effective force generated at the bit face is significantly multiplied. The vibrational force causes soil particles along the side of the drill to fluidize or break apart from the surrounding ground. The term xe2x80x9csonic drillingxe2x80x9d stems from the fact that the frequency of vibrations normally used is in the 50-200 Hertz range, which is within the lower range of audible sound that can be detected by the human ear. In addition to earth probing, vibrational force can be used to facilitate installation of other objects into the ground.
Various techniques are available for providing the vibrational force necessary for sonic drilling. One method is a direct-drive vibration machine.
An example of a sonic drill utilizing a direct-drive mechanical vibration or brute force mechanism is shown in U.S. Pat. Nos. 5,027,908 and 5,409,070 both to R. Roussy, incorporated herein by reference. The Roussy design features a motor connected to and driving a horizontal shaft through a pair of splined gears. The shaft is connected to a crank by means of a second shaft having ball ends with splined connections. A pair of the cranks drive offset counter rotating rollers. Each roller is housed in a cylindrical cavity. The offset rollers provide a cam movement to the following cylindrical cavities resulting in a vibrational up-and-down motion of vertical shafts and the drill string.
According to one embodiment of the present invention, four eccentric masses are rotatably mounted in a sine generator housing, with each of the masses offset from an adjacent mass by 90xc2x0, so that the four eccentric masses are on mutually perpendicular intersecting axes, which also intersect the axis of the spindle. A spiral bevel gear drives two of the eccentric masses through gear teeth on the masses, and the driven masses drive the other two masses through corresponding gear teeth. The spiral bevel gear is rotated by a drive shaft which connects the spiral bevel gear to a speed increaser assembly mounted on the outer housing. The drive shaft allows for parallel, axial, and angular misalignment with respect to the spiral bevel gear and the speed increaser assembly, which is driven by a drive motor. In one embodiment, the drive shaft is connected to the spiral bevel gear and to a speed increaser pinion through splined connections and is biased vertically by a pack of disc springs, to preload upper and lower retainers mating with spherical surfaces of an end of the shaft. The spindle is rotated by a separate rotary drive motor, which drives a drive gear connected to the sine generator housing. The rotary drive motor is mounted to an outer housing and separated from the sign generator assembly by a pack of precision disc springs. Another set of precision disc springs are mounted between the drilling spindle and another bearing that is supported by the housing. Together, these packs of precision disc springs isolate the drive mechanisms and the outer housing from the vibrations of the sine generator.
These and other features of the present invention will become apparent from the following description, with reference to the accompanying drawings, in which: